1. Field of the Invention
The present invention relates to a linear actuator which displaces a movable body linearly with electromagnetic force. More specifically, the present invention relates to a linear actuator capable of driving said movable body at low seeds.
2. Description of the Related Art
There has long been known a linear actuator which drives a load by displacing a movable body linearly with electromagnetic force. The linear actuator of this type usually consists of an exciting coil, a core which generates electromagnetic force when the exciting coil is energized, and a movable body which is displaced by electromagnetic force as thrust force which is supplied from said core.
The linear actuator mentioned above is usually so constructed as to be driven with a large thrust force in order that said movable body is displaced surely and stably against load and sliding resistance. Consequently, said movable body moves at a high speed and produces noise when it collides violently against the stroke end. One way to reduce noise was by using a rubber damper which absorbs shocks to the movable body. However, this poses a problem with durability and dusting.
There have been proposed several techniques to address the above-mentioned problem by controlling the driving speed of said linear actuator. For example, Patent Document 1 discloses a method for controlling the driving speed by detecting how the movable piece of the linear motor changes with time in stroke and speed with the help of a measuring apparatus (displacement sensor), comparing the detected data with a characteristic curve which has previously been established in a control apparatus, and regulating the target of electric energy according to the difference between the detected value and the characteristic curve. However, this method needs a displacement sensor and a complex control circuit, which inevitably makes the actuator larger and the control unit more complex. Patent Document 1: Japanese Patent Laid-open No. 2001-23818